Some of Britain's leading hospitals stand accused of exploiting the coalition's controversial lifting of the cap on the number of private patients they can treat to increase their income as part of a "creeping privatisation" of the NHS.

As new figures show that some hospitals have seen a big increase of up to 40% in their private income since the cap was lifted, Labour accused ministers of presiding over a scandal of declining standards for NHS patients while allowing paying patients to enjoy high standards of care.

The determination of NHS trusts to make the most of the cap being lifted has been highlighted by the decision of the Royal Brompton Trust, a centre of expertise in treating heart and lung disease, to open a "private outpatient facility" in Harley Street, the world centre of private medical treatment. But less than a mile away from the Brompton Hospital, at the Chelsea and Westminster Hospital on the Fulham Road, west London, there is concern about the implementation of the lifting of the private patient cap. Its annual report lists it as one of the "principal risks and uncertainties facing the trust".

Hospitals were given the right to generate up to 49% of their income from private patients under the terms of the Health and Social Care Act, which was the former health secretary Andrew Lansley's brainchild. Under the rules introduced by the last Labour government for foundation hospitals, the amount of private income was capped at the level reached in 2006. This averaged about 2% around the country but there were regional variations, with higher rates in London.

New figures released under the Freedom of Information Act show that six trusts in London and the south-east have hugely increased their private patient income since the passage of the Health and Social Care Act in 2012. The figures, released to the shadow minister for London, Gareth Thomas, showed an increase in private patient income at:

• University College Hospital Trust in London by 39.63% – from £7.3m in 2010‑11 to £10.3m in 2013‑14.

• Royal Brompton Hospital Trust in London by 37.7% – from £24.3m to £33.6m.

• Moorfields Eye Hospital in London by 31.84% – from £16.1m to £21.3m.

• Papworth Hospital Trust in the South Cambridgeshire constituency of the former health secretary Andrew Lansley by 29.9% – from £4.9m to £6.4m.

• Royal Surrey County Hospital Trust, which serves the South West Surrey constituency of the health secretary, Jeremy Hunt, by 25.6% – from £3.6m to £4.6m.

• Chelsea and Westminster Hospital Trust in London by 20.99% – from £10.7m to £13m.

Thomas told the Guardian: "When more people are waiting on trolleys or waiting longer to see their GP, it is a scandal that top hospitals are allowed to prioritise increasing income from private patients. Lifting the cap on the level of private patient income is just one further example of the creeping privatisation of NHS services."

"Ministers said that lifting the cap wouldn't make a dramatic difference. What is quite clearly the case is that a number of NHS hospitals have rapidly expanded their private patient services at the same time as services to NHS patients have deteriorated."

He was highly critical of the Royal Brompton Hospital Trust, which boasts in its annual report of how it has "built a significant private patient business" that has exceeded £30m for the first time. The report said the trust had created a special logo for private patients and said it would open a clinic in Harley Street to improve "brand awareness".

The annual report said: "The trust considers that a presence in the Harley Street area of London would increase both brand awareness and market share within central and north London as well as from international patients. With this in mind, the trust intends to open a private outpatient facility in that area in the coming year."

Thomas said: "Hospitals have gone out of their way to exploit the lifting of the private patient cap at the same time as waiting lists have got longer and services in A&E have got worse. This sounds like Brompton hospital has lost sight of the fact that they are an NHS hospital first and foremost, and they should prioritise the needs of NHS patients, not building up more private patient income."

But the Chelsea and Westminster Hospital Trust raised concerns about the implementation of the private patient cap. It said in its annual report: "There remain uncertainties around the impact of the practical implementation of the Health and Social Care Act, in particular the transfer of responsibility for commissioning services to GPs, the relaxation of the private patient income cap, more choice for patients and increased competition. The overall trust strategy has taken these issues into account and plans are in place to mitigate and/or benefit from these changes." The report added: "Private income currently accounts for 5% of the trust's overall income.Tony Bell OBE [chief executive] on 25 February 2014 said he would like the trust to increase this figure. We trust that any concentration on promoting the most profitable services do not have any negative impact on the NHS clinical services the hospital provides."

Government sources said the increase in private patient income, which has to be invested in NHS services, was unsurprising in leading London hospitals, which have a lengthy history of treating private patients from around the world.

The income from private patients in English NHS trusts as a whole has barely changed since the lifting of the cap. Income from private patients accounted for 0.69% of overall provider income in England 2012-13, rising slightly to 0.7% in 2013-14. It stood at 0.71% in 2010-11 and 0.68% in 2011-12.

A government spokesman said: "Hospitals are treating record numbers of NHS patients, with 850,000 more operations being carried out each year than under the last government. NHS hospitals have always been able to generate small amounts of additional income – which has remained well below 1% of hospitals' total income in the last four years – by treating private patients, every penny of which is used to improve the services that NHS patients receive."

A spokesman for the Papworth Hospital Trust said: "Papworth Hospital is internationally renowned for cardiothoracic care and subsequently attracts patients both within the NHS and those looking for private healthcare. Although private practice does complement the lifesaving services provided at Papworth Hospital, it makes up just 5% of the overall activity, which is below the current and previous allocated private patient allowances set by government. Revenue generated from private practice at Papworth Hospital supplements patient care and research to further develop lifesaving treatments that benefit thousands of patients every year."

A spokeswoman for Moorfields said: "Moorfields' main focus is the treatment of NHS patients and our private patient activities exist to entirely to augment and support the care we provide to NHS patients. Changes to the cap enabled the trust to pursue our strategy for growth in our commercial activities, which includes, but is not limited to, treating private patients in the UK so as to generate more income for reinvestment in services for NHS patients, without impacting on our NHS activity. Although our private patient income has increased it represents 12% of our total income in 2013-14 as compared to 13% in 2010-11."

The Guardian approached the Royal Brompton Hospital Trust, Chelsea and Westminster, University College Hospital, and Royal Surrey for comment but none had responded at time of publication.